Get a vertex that is on a specific edge
If you don't want to use BMesh, the following will work:

import bpy

data = bpy.context.scene.objects.active.data
edges = data.edges     # collection of all edges
verts = data.vertices  # collection of all vertices

# must be in object mode of course
bpy.ops.object.mode_set(mode = 'OBJECT')

# the indices given by MeshEdge.vertices correspond to the collection of vertices
verts[edges[0].vertices[0]].select = True

# go back into edit mode to see the new selection
bpy.ops.object.mode_set(mode = 'EDIT')


BMesh can be a bit simpler though...

import bpy
import bmesh

data = bpy.context.scene.objects.active.data

bm = bmesh.from_edit_mesh(data)
bm.edges[0].verts[0].select = True